The present invention relates to a heat treatment apparatus for performing heat treatment of a sheet which must be treated, and more particularly to a heat treatment apparatus for use to, with heat, develop a material having an image formed thereon in a dry system which does not require a wet process and which uses a dry material.
The wet system has been employed in, for example, an image recording apparatus for printing a plate, a digital radiography system arranged to use a heat accumulative fluorescent sheet, and an image recording apparatus for recording an image for medical use, such as CT or MR. The wet system is arranged to photograph or record an image on a silver-salt photosensitive material, followed by performing a wet process so as to obtain an image.
On the other hand, a different recording apparatus has attracted attention. The recording apparatus employs a dry system which does not require the wet process. In the recording apparatus of the dry type, a photosensitive and/or a thermal recording material (a thermal and photosensitive recording material) or a film (hereinafter called a xe2x80x9crecording material) constituted by a thermal development photosensitive material is employed. The recording apparatus using the dry system incorporates an exposing portion for irradiating (scanning) the recording material with a laser beam to form a latent image. Then, a thermal development portion of the system brings the recording material into contact with a heat means to perform thermal development. Then, the recording material having an image formed thereon is discharged to the outside of the apparatus.
The dry system is able to form an image in a shorter time as compared with the wet process. Moreover, the necessity for disposing waste solution required of the wet process can be overcome. Therefore, increase in the demand for the dry system has been expected.
A portion of the foregoing conventional dry system has a structure that the heat development portion incorporates, for example, a heating means and a pressing/moving means to hold and move the recording material by the heating means and the pressing/moving means so as to perform heat development. That is, the recording material is heated to a predetermined temperature so as to be developed with heat when the recording material is held and moved between the heating means and the pressing/moving means. If the recording material cannot be heated sufficiently at this time, uneven development occurs. Since the recording material for dot printing has high sensitivity because a dot image for printing must have excellent image quality, the image quality considerably deteriorates if heating cannot be performed to the predetermined temperature. It leads to a fact that a temperature sensor has been provided for the heating means so as to accurately control the temperature in accordance with the temperature detected directly.
The heating apparatus has an inspection cover which is sometimes opened and closed owing to occurrence of a jam or the like. Thus, the heat development portion is cooled to the outside air temperature. In the foregoing case, the temperature is lower than the predetermined temperature for some time even after the inspection cover has been closed. It leads to a fact that the heating means incorporating the provided temperature detection sensor directly detects the decrease in the temperature. Therefore, the temperature can relatively quickly be returned to the predetermined temperature. On the other hand, the other members in the heat development portion except for the heating means are returned to the predetermined temperature at individual raising rate. Therefore, when the temperature is again raised after interruption of heating, the temperatures of members which concern the heat development must accurately be detected. Moreover, control must be performed such that the temperatures of the members are returned to the predetermined temperature.
The pressing/moving means which is brought into contact with the recording material in a direct manner exerts a great influence of the temperature thereof on the development temperature. To maintain frictional force with the recording material, the pressing/moving means is coated with a silicon rubber or the like. Therefore, temperature sensor cannot directly be brought into contact with the pressing/moving means. Thus, the temperature of the pressing/moving means cannot be detected. Hence it follows that there is a requirement for detecting the temperature of the pressing/moving means to realize more accurate control of the temperature in the heat development portion.
In the dry system, the thermal development portion is usually provided with a heat drum which serves as a heating means. An endless belt is wound around the heating drum for a predetermined angle. Thus, the heating drum and the endless belt are used to hold and move the recording material to perform the heat development. If the endless belt cannot maintain uniform tension, required contact between the recording material and the heating drum cannot be established. Thus, uneven development occurs.
Since a dot image which must be printed is required to have excellent image quality, the sensitivity of the recording material has greatly been improved. Therefore, unsatisfactory contact with the heating drum encounters excessive deterioration of the image quality.
The heating means encounters a problem in that the temperature is decreased at an end portion to which heat cannot sufficiently be supplied. Moreover, the heating means suffers from undesirable bending and occurrence of a wrinkle caused from buckling of an end portion of the recording material which takes place when the recording material is held between the heating drum and the endless belt. The wrinkle becomes conspicuous in a case where a recording material (for example, a recording material for making a plate for a newspaper) of a type having a large size and great thickness is used.
An object of the invention is to enable more accurately control of the temperature of a heat development portion to be performed by employing a structure which is capable of detecting the temperature of the pressing/moving means.
Another object of the present invention is to provide a heat treatment apparatus which is capable of making the contact between the heating member and a recording material to furthermore be uniform, preventing occurrence of a wrinkle, realizing furthermore uniform heating and therefore capable of forming an image exhibiting high quality free from uneven development.
A heat treatment apparatus according to the present invention comprises:
a heating member which subjects a sheet to a heating process at a predetermined temperature;
moving means which moves the sheet;
a temperature-measured member, the temperature of which is measured and changed with a relationship with change in the temperature of the moving means and which is provided at a position adjacent to the moving means;
a temperature sensor disposed in contact with the temperature-measured member so as to measure the temperature of said temperature-measured member; and
temperature control means which controls the temperature of the moving means in accordance with a result of detection of the temperature performed by the temperature sensor.
The heat treatment apparatus incorporates the temperature sensor with which the temperature of the temperature-measured member is measured. The detected temperature is corrected in accordance with the relationship between change in temperature of the moving means and a change of a temperature of the temperature-measured member. Therefore, the temperature of the moving means which cannot be detected by the conventional technique because direct contact has been inhibited can be detected. It leads to a fact that accurate control of heating corresponding to the detected temperature of the moving means can be performed. Therefore, a predetermined temperature of the moving means can be maintained. If the temperature of the moving means is changed, the temperature can quickly be restored to the original temperature.
A heat treatment apparatus according to the present invention has a structure that the moving means is structured by coating the outer surface of a roller with an elastic member having a predetermined thickness,
the temperature-measured member is structured by coating with an elastic member constituted by the same material as the material of the elastic member with substantially the same thickness, and
the temperature sensor is disposed in contact with the surface of the elastic member of the member, the temperature of which is measured.
The heat treatment apparatus has the structure that the member, the temperature of which is measured, is composed of the same component as the component of the moving means. Therefore, change in the temperature of the heating drum is made to approximate change in the temperature of the moving means. As a result, the difference between the temperature obtainable from the temperature-measured member and the actual temperature of the moving means can be reduced. Hence it follows that the estimated temperature of the moving means can accurately be detected.
A heat treatment apparatus according to the present invention has a structure that the moving means is a pressing/moving means which slides and moves the sheet on the surface of the heating member while pressing at least a portion of the sheet against the surface of said heating member.
Since pressing/moving means of this heat treatment apparatus slides and moves the sheet on the surface of the heating member while pressing at least a portion of the sheet against the surface of said heating member, the wrinkle which occurs in the sheet A is prevented.
To achieve the foregoing object, according to one aspect of the invention, there is provided a heat treatment apparatus comprising:
a heating member for subjecting a sheet to a heating process at a predetermined temperature at a predetermined position;
a pressing/moving means for sliding and moving the sheet on the surface of the heating member while pressing at least a portion of the sheet against the surface of the heating member; and
a cushion member provided for the surface of the heating member and arranged to moderate the pressure which is exerted from the pressing/moving means on the sheet.
In the heat treatment apparatus, when the sheet which has been introduced into a space between the cushion member and the pressing/moving means is pressed by the pressing/moving means, the cushion member is elastically deformed. Thus, deformation of the sheet is permitted. Moreover, reaction from the cushion member is exerted on the sheet. It leads to a fact that a partial tension is given to the sheet. As a result, a wrinkle is formed in the sheet can positively be removed.
A heat treatment apparatus according to the present invention further comprises a pulling means for giving a tension to the cushion member.
In the heat treatment apparatus, the cushion member is pulled by the pulling means so that a tension is always exerted on the cushion member. Therefore, if the relative position between the heating member and the cushion member is deviated owing to the difference in the coefficient of thermal expansion, occurrence of a wrinkle can be prevented.
A heat treatment apparatus according to the present invention has a structure that the cushion member is detachable from the heating member.
The heat treatment apparatus according to the present invention incorporates the cushion member which is detachable from the heating member. Therefore, if fatigue of the cushion member occurs, employment of a new cushion member permits the function capable of moderating the pressure of the pressing/moving means to permanently be maintained.
A heat treatment apparatus according to the present invention has a structure that the cushion member is a fiber sheet constituted by gathering fine thread materials.
The heat treatment apparatus according to the present invention has the structure that the cushion member is a fiber sheet constituted by gathering fine thread materials. Therefore, for example, employment of the following fibers is permitted: natural fibers (including vegetable fibers, animal fibers and mineral fibers) and chemical fibers (including regenerated fibers, semi-synthetic fibers, synthetic fibers and inorganic fibers). Therefore, the material can widely be selected to satisfy required low-friction, heat resistance, elasticity and low cost.
A heat treatment apparatus according to the present invention further comprises a sub-heating member disposed opposite to the heating member across the moving means.
The heat treatment apparatus further comprises the sub-heating member disposed opposite to the heating member across the moving means. Thus, the difference between the temperature of the right side and the temperature of the reverse side of the sheet can be reduced. Thus, the sheet can furthermore uniformly be heated. As a result, uneven development can be prevented.